Transmission line having dead-end portion



March 4, 1947. i w,-GEQRGE 2,416,827

TRANSMISSION LINE HAVING DEAD END PORTION Filed June 9, '1943 v lNVENTOPJ aYphWGeonge 5 mm/ ArroPA/EK Patented Mar. 4, 1947 TRANSMISSION LINE HAVING DEAD-END PORTION Ralph George, Riverhead, N. Y., assignor to Radio Corporation of America, a corporation of Delaware Application June 9, 1943 ,'Serial No. 490,225

Claims. 1

This invention relates to improvements in adjustable resonant transmission line circuits such as are used at ultra high frequencies.

In employing tunable resonant transmission line circuits, such as concentric lines and lecher wires, it is customary to tune the circuit by means ofan' adjustable short-circuiting bar or bridge which is movable ove.r1 the length of the conductors. In this typeof circuit difliculties are sometimes experienced from, the dead end or unused portion of the resonant line due to the effect of resonance in' this unused portion which has some finite coupling with the main portion of the resonant line.

When such a resonant transmission line is employed in an ultra high frequency oscillation generator tunable over a relatively wide frequency range, there may be experienced dead spots or undue losses at certain frequencies in the tuning range. This trouble is due primarily to the aforementioned resonance effects in the unused portions of the conductorsof the transmission line.

A primary object of the present invention is to eliminate or reduce, to a considerable extent, the influ ence of the dead end or unused portion of the tunable resonant transmission line on the desired or useful portion ofthe line. Putting it in other words, an object is to prevent the influenceof those portions of the conductors of the line beyondthe-short-circuit bridge from affecting the normal operation of the system connected to the useful portion of the line.

Another object is to provide an improved ultra high frequency oscillation generator having resonance transmission line circuits and. which is tunable in a continuous manner over a relatively wide frequency range so that satisfactory operation is obtainable'througho'ut the entire frequency range.

A further object is to provide a tunable signal generator having adjustable resonant transmission lin circuits and which is capable of satisfactory operation over all points of a frequency range on the order of 550 to 1400 megacycles. A feature of the invention lies in theuse of a parallel conductor transmission line circuit having an adjustable sho'rt-circuitin'g slider. One end offthe circuit is connected to an energizing unit'andthe. otherendv is connected to a D. C. circuit". A damping resistor is placed at a suitable." point on the unused portion of the transmission line'fcircuitlfor the, purpose of damping undesirable resonance effects.

Another feature lies in the use of a transmission line circuit having a pair of parallel of an angle-shaped member and the other conductor of which is in the form of a rod suitably placed within the sides of the angle formed. by

said member. One side of the angle member is provided with a slot extending substantially over its length and which slot guides a slider for connecting the rod to the angl member. Suitably placed short-circuiting straps are connected over the length of the angle member between the two sides thereof for .preventing resonance from building up in the slotted member at frequencies near the operatng frequency of the system.

Further objects and features will appear here after.

A more detailed description of the invention follows in conjunction with th drawing, wherein Figure 1 illustrates one embodiment of an oscillator generator constructed in accordance with the principles of the invention; Figure 2 illustrates a detail of the short-circuiting slider along the line 2-2. of Figure 1; and Figure 3 is a plan view of the short-circuiting slider asv seen looking down on the transmission line circuit of Figure 1.

Referring to Figure 1, in more detail, there is shown an oscillator generator comprising a three electrode vacuum tube I 0 having a grid ll, an anode l2 and a filament l3. The circuit of the oscillator generator, except for the improvements to b hereafter noted, is similar to the oscillatory generator described in and illustrated in Figure 4 of my copending application, Serial #408,570, filed August 28, 1941, now U. S. Patent No. 2,399,481, granted April 30, 1946. The grid, anode and filament electrodes have individually associated therewith adjustable resonant transmission lin circuits, as will hereinafter be described, as a result of which high frequency oscillations are produced over a relatively wide frequency range; for example, over a range from 550 to 1400 megacycles.

The grid and anode tuned circuits each'comprise an adjustable transmission line circuit having an angle-shaped member [4 and a rod l5 placed substantially symmetrically within the sides of the angle formed by the member I4. The conductors l4 and I5 of each tuned circuit are of high electrical conductivity andmay be copper plated with silver or gold. The vertical side of the angle member I4 is provided with a slot l6v which extends substantially over its entire length, as shown, and which serves to guide a movable short-circuiting slider or bridge. Both the grid and the anode transmission line circuits lengths of the slots.

may be compared to a concentric transmission line wherein part of the outer conductor [4 has been removed and wherein rod 15 constitutes the inner conductor. The inner conductor I5 is mechania provides improved operation at medium and high frequencies over the tuning range.

The filament 13 of vacuum tube I0 is shown connected to a filament supply circuit through a tunable coaxial transmission line system 48. A suitable slider 29 serves'to tune the filament by connecting any desiredportion of the outer concally supported from the outer conductor at the end removed from the vacuum tube. Ill'by means of an insulating block i9. slider is drivenjby means of an insulation block threadedly engaging a, lead screw 2|. This slider serves to bridge or connect the conductors l4 and I5 as it moves along the length of the transmission line under control of the lead screw in amanner described in more detail hereinafter in connection with Figures 2 and 3.

To prevent resonance from building up in the side portions ofthe'slot 16 at frequencies near the operating frequency of the oscillation generator, there are provided for each transmission line apair of metallic short- -circuiting straps 22, 22 whichconnect the side edges of the angle mem her. The straps 22, 22 effectively short-circuit the sides of the slot and thus divide the slot into circuits which have resonance frequencies considerably higher than the operating frequency of the' system; It'will be seen that these straps are so arranged that they do not interfere with themechanical operation of the sliders along the A damping resistor 23 is provided at each end of the grid and anode line sections which is removed from the vacuum tube todamp the resoname in the dead end or unused portion of the line i4, i5. This unused portion is that part of the transmission line which appears between the short-circuiting slider and the end of the line adjacent insulating block H2. The resistor 23 is bridged between the conductors. l d, i5, as shown, and has' a rather low resistanoegvalue of the order of the characteristic impedanceof theiine'J portion of the line between the slider and thea D. C. circuit. The grid is supplied with a suitable bias by way of lead 2 3 and grid leak 2-5. The anode is supplied with a polarizing potential byway of lead 26 and low pass filter 41, one end of which is connected to the positive terminal +B of a source of anode potential. "The lengths of the leads 24 and 26 will afiect the. effectiveness of the damping resistor and will indicate -whethe shunt or series damping should be used. E In order to more efiectively tie together th outer conductors M of the anode and grid trans mission line circuits at the ends near the tube electrodes, there has been provided an added capacity between these two outer conductors in 'the' form of a strip of metal 21, which is' directly connected to one of the conductors It and capa'citively coupled to the' other conductor M by means of-a mica" spacer 28.] If desired, this metal strip 2.! can be'replacedl by a condenser of con vntional construction. 1 I This auxiliary capacity A short-circuiting ductor of the coaxial line-48 to a suitable ground plate 30. In practice, ground plate 30 can form part and parcel of the base'plate H. The filament tuning system, if desired, may employ an adjustable transmission line circuit identical with conductors l4 and I5 and with a short-cir- .1 cuiting bar or slider arrangement similar to that shown for the transmission line circuit I 4, l5.

Reverting to the consideration of the short-circuiting slider for'the transmission line circuit M, iii, it will be seen that both lead screws 2! are unicontrolled by means of a dial 3|. The mechanical connections between the lead screws are shown in conventional manner by the dash lines 32 and may comprise any suitable'mechanical arrangement.

Figure 2 illustrates a side view of the slider construction for the transmissionline circuit l4, I5 along the line 2-2 ofFigure 1. The slider, in l effect; comprises upper and lower contact members 33 in engagement "with the rod l5. Members 33 preferably have a silver inlay for contact purposes secured to a brass T-shaped slider 34 whose central arm passes through the slot i6 for cooperation with an insulation block 20 through which the lead screw passes. The slider 34 is held in contact withthe sides of the slot by means of a beryllium copper spring 35 which accommodates steel balls 36 0n both sides of the slot. On the inner'side of the angle member I 4 there are provided silver inlays 31 for maintaining good electrical contact betweenthe conductor l4 and the brass member 34. In effect, there are two contact members 33 above conductors I5 and two similar contact members be low conductor IS in corresponding positions. This is seen more clearly from an inspection of Figure 3. The slider is so designed that the ele-' merits, when assembled, maintain good electrical contact pointsvin spite of irregularities in align ment of the parts. V 1

The grid and anode electrodes of the tube Ill are provided at the sideof the envelope removed from the transmission line'circuits I 4, l5 with fixed inductor elements comprising concentric line sections 38, 38. The inner conductors of the concentric line inductors are capacitively coupled to the grid and anode electrodes, respectively, through blocking condensers 39. These fixed inductors serve to complete the oscillation generator circuit. A suitable output circuit, here shown as a loop 40, enters the interior of" one of the fixed concentric inductor lines 38 to derive output energy from the'generator. Inone embodiment of the invention tried out in practice in connection with a signal generator, vacuum tube in was aW. E. 368-A tube. The signal generator functioned over a tuning range from approximately 550 to 1400 megacycles, al

though the vacuum tube employed in this embodiment was of the type wherei the grid and anode electrodes were each provided with a pair of terminals extendingfrom opposite sides of the envelope. it should be understood that thisparg ticular embodiment was employed primarily for obtaining thehigh frequencies and the widefrequency range desired. Obviously, the features of the invention an" be employed in connection with other oscillation generator systems wherein similar difficulties due to undesired resonance effects of the unused portions of tuned transmission line circuits are encountered.

What is claimed is:

1. A high frequency system comprising a pair of parallel conductors forming a tuned transmission line, a short-circuiting bar intermediate the ends of said line for tuning a circuit connected to one end thereof, and a damping resistor of the order of the characteristic impedance of the line in circuit with the other end of said line for damping oscillations therein.

2. A high frequency system comprising a pair of parallel conductors forming a tuned transmission line, a short-circuiting bar intermediate the ends of said line for tuning a circuit connected to one end thereof to a desired frequency, one of said conductors having a slot therein along the length thereof for guiding said short-circuiting bar, and fixed means for bridging said slot at a plurality of points along its length.

3. A high frequency system comprising a pair of parallel conductors forming a tuned transmission line, a short-circuiting bar intermediate the ends of said line for tuning a circuit connected to one end thereof to a desired frequency, one of said conductors having a slot therein along the length thereof for guiding said shortcircuiting bar, a damping resistor in circuit with the other end of said line, and fixed means for bridging said slot at a plurality of points along its length.

4. A high frequency system comprising a pair of parallel conductors forming a tuned transmission line, a short-circuiting bar intermediate the ends of said line for tuning a circuit connected to one end thereof to a desired frequency, one of said conductors having a slot therein along the length thereof for guiding said short-circuiting bar, and a plurality of metallic straps bridging said slot at a plurality of points along its length, to thereby cause the resonant frequency of any portion of the slot member to exceed the operating frequency of the system.

5. A system in accordance with claim 4, characteristic in this, that the conductor having the slot is in the form of an angle-shaped member, while the other conductor is a rod located within the angle formed by the sides of said member.

6. A high frequency system comprising a vacuum tube having a pair of cold electrodes, individual tunable transmission lines'for said cold electrodes, each of said lines having substantially along its entire length one conductor connected through a path of low impedance at radio frequency to ground, and a capacity providing still lower impedance between those ends of said last conductors which are nearest said cold electrodes.

7. A high frequency system comprising a vacuum tube having anode and grid electrodes, separate tunable transmission lines connected at one end to each of said electrodes, said lines being parallel to each other and extending on the same side of said tube, a common ground plate, a ca pacity connection from one conductor of each of said lines to said common ground plate, and an auxiliary capacity connection between the ends of said one conductors at the location nearest said electrodes.

8. A high frequency system comprising a pair of parallel conductors forming a tuned transmission line, a sho-rt-circuiting bar intermediate the ends of said line for tuning acircuit connected to one end thereof to a desired frequency, one of said conductors having a 'slot therein along the length thereof for guiding said short-circuiting bar, a damping resistor in circuit with the other end of said line, and fixed means for bridging said slot at a plurality of points along its length, said circuit comprising a vacuum tube having an electrode connected to said line.

9. A high frequency system comprising a vacuum tube having anode and grid electrodes, separate tunable transmission lines connected at one end to each of said electrodes, said lines being parallel to each other and extending on the same side of said-tube, a common ground plate, a capacity connection from one conductor of each of said lines to said common ground plate, an auxiliary capacity connection between the ends of said one conductors at the location nearest said electrodes, and damping resistors in shunt to said lines at their ends remote from said vacuum tube.

10. An ultra high frequency system comprising a vacuum tube having a pair of cold electrodes, individual tunable transmission lines connected at one end to said cold electrodes, a movable short-circulting slider intermediate the ends of each line for tuning the same, saidlines being parallel and located on the same side of said tube, each of said lines having one conductor connected through a path of low impedance at radio frequencies to ground, a capacity providing still lower impedance between said one conductors at these ends nearest said vacuum tube, a damping resistor for each of said lines at a location near the end remote from said vacuum tube, Said resistor having a value of the order of the characteristic impedance of the line to which it is connected, said one'conducto'r of each line having a slot for guiding the slider associated with the REFERENCES CITED The following references are of record in the file of this patent:

UNITED STATES PATENTS Number Name Date 2,051,520 Evans Aug. 18, 1936 2,203,481 Zottu June 4, 1940 2,270,949 Hulster Jan. 27, 1942 1,894,134 Tonks Jan. 10, 1933 2,135,672 a Morris Nov. 8, 1938 2,223,160 Alford Nov. 26, 1940 

